The ability to provide long-distance wireless communication in dangerous and/or obstructed environments, for example in underground mines, is essential for both efficient operation and safety. In some applications, such as coal mining, communication systems are required by regulations for post-accident communications. In these environments, transmitting communication signals through earth, water and rock, for example, in addition to the large amounts of steel and concrete used in associated structures, severely impacts the effective range of a communications signal.
Waveform attenuation can be a significant problem in these embodiments as the sampling clocks in a transmitter and receiver of the communication system are not precisely synchronized. The lack of sampling clock synchronization can result in an undesired frequency shift/stretch of the carrier frequency which can generate an undesirable signal to noise ratio (SNR) penalty. While a phase-locked loop control system or similar feedback control mechanisms can be implemented in the communication system to recover the carrier frequency, these systems can be complex, expensive and may not provide carrier recovery when the communication system is operating at a very low signal to noise ratio.